1. Field of the Invention
This invention pertains generally to well screens for oil, gas, mineral, and groundwater production, and groundwater monitoring, and more particularly to an improved one piece wire-wrapped well screen.
2. Description of the Background Art
When water, oil and gas producing wells are drilled through unconsolidated formations, the produced fluids generally contain particulate matter, usually sand. The production of sand, along with the fluids, is an undesired consequence because the sand causes extra wear and abrasion of production tubing, valves, pumps, and other equipment used to produce and remove fluids from the wells. It is therefore beneficial to avoid or minimize the production of sand or other particulate matter during the production of fluids from wells.
One method of accomplishing the reduction of sand or particulate production is by "gravel packing" the well during completion operations. Such gravel packing includes providing on the production conduit or tubular work string a slotted or ported cylindrically shaped member, generally known as well screens, which restricts the passage of particles into the interior of the conduit. For many years, well screens have been used in wells to permit fluid to flow through the screen and into the well while retaining sand and other particulate matter outside the well screen.
A common well screen design uses longitudinal supports tangentially welded to a helical band to produce a frame upon which strainer elements or inserts are attached. The strainer elements or inserts fill the gaps between the longitudinal and helical bars and serve to retain sand and other particulate matter. In such designs, the filtration screen is not self-supporting and is dependent on the frame for rigidity.
Other designs of well screens incorporate "projections" that are formed in a stack of rings and which protrude parallel to the longitudinal axis of the structure and perpendicular to the rings. This enables installers to adjust the gap between the rings during installation of the well screen. However, the projections do not provide structural rigidity to the screen and merely rest on the inner surface of the rings, thereby resulting in an undulated inner well screen surface.
Current screen design practice assumes a 1% ellipticity, which significantly reduces collapse strength and requires use of excess materials in order to achieve the desired resistance. The general tensile calculation for conventional wire wrap screens includes an approximate 30% welding de-rating effect due to welding of the wire or ring apex to the rod tangent, which is also a corrosion enhancer. Wire/rod screens have no torsional qualities. Corrosion, well construction defects, or manufacturing errors occasionally lead to holes or cracks in well casings or screens. One approach toward repair is to spot a serrated piece of slightly under-sized casing and hydraulically pressing this piece over the problem area, essentially forming a patch. This is impractical due to the presence of vertical rod protrusions in conventional wire wrap screens.
Conventional wire wrap screens normally show mostly steel, not open area available for fluid to flow through. The usual range of open area percentage exposed to abutting geological formations is 20%-50% with a fluid entrance efficiency of approximately 90% at best.